In a typical automobile engine, an endless timing chain is used to transmit rotation from an engine crankshaft sprocket to one or more engine camshaft sprockets. The chain is typically in sliding contact with two chain guides, one being a stationary guide fixed to the engine, and the other being a movable guide in the form of a pivoted tensioner lever which cooperates with a tensioner to control chain tension. In each of the two kinds of chain guide, the chain travels longitudinally in sliding contact with a front surface of an elongated shoe. A base plate supports the back surface of the shoe. Together, the shoe and base plate prevent deformation and breakage of the chain by constraining the chain so that it does not deviate from a plane of travel, and so that it travels along a path having a predetermined curvature. An example of a typical chain guide is described in Japanese Laid-Open Patent Publication No. Hei. 10-292855.
Even if the base plate of the guide is made of steel, it is likely to undergo deformation and breakage due to excessive loads applied to the guide by the chain, specially in the high temperatures environment in an engine, where the temperature can exceed 200° C. The strength of the base plate can be enhanced by the use of more durable materials, but the use of such materials leads to a significant increase in manufacturing costs. Increasing the thickness of the base plate is another measure that can be taken to avoid deformation and breakage of the base plate, but increasing the thickness of the base plate is often not a desirable option because of limited space in the engine.
Accordingly, an object of the invention is to provide a chain guide, which reliably maintains a predetermined path of travel of the chain without the need for a thick base plate, and in which deformation and breakage of the base plate are avoided even when the chain guide is subjected to large forces under high temperature operating conditions in an engine.